The Web Cache Communication protocol (WCCP) is a content-routing protocol that provides a mechanism to redirect traffic flows in real-time. It allows utilization of engines or other caches running WCCP to localize web traffic patterns in the network, enabling content requests to be fulfilled locally. Traffic localization reduces transmission costs and download time.
WCCP works by placing a WCCP capable router/switch in between users and the internet, either in the path or as the default gateway. The WCCP device will then transparently redirect traffic on the ports that are configured over to a Web Gateway for filtering and proxying. The user has no idea that the Web Gateway is in place as all traffic is sent from the Web Gateway directly back to the user while spoofing the server's IP address.
In practice, when a client device requests a webpage, instead of going outside the local area network (LAN) to the internet, the request is sent to a router/switch which redirects the traffic to a cache engine (CE). The CE includes a database or cache of previously accessed webpages. It caches all or a portion of the most recently accessed webpages and handles requests from the switch/engine. Accordingly, if the webpage the client device is requesting is included within the cache, the webpage is fetched from the cache instead of the internet. If the webpage is not included within the cache, the request goes back to the router/switch and then on to the internet, where the webpage is saved on the cache for subsequent use. This allows bandwidth to be used judiciously.
However, traffic redirection to the CE can be rejected for reasons beyond that the website has not been accessed before. The CE might be temporarily overloaded, cannot handle the types of packets included in the traffic, is in maintenance, etc. No matter the reason, though, the traffic takes the same path as if it is initially accessing the website. This causes unnecessary processing on a continuous basis, as the router/switch keeps sending packets to be rejected by the CE, using expensive resources (such as TCAM lookups) until the traffic is either manually redirected to the internet or the processing issue is finally resolved.